In bioimaging, characterization, e.g., detection and/or diagnosis of particular cells within an environment, such as within a patient, is useful for many reasons as will be appreciated in the art. However, widely used methods for characterization of cells have certain drawbacks.
As a nonlimiting example, X-ray mammography is a known method for breast cancer detection, but X-ray mammography has low sensitivity for younger women (e.g., <40 years) due to their dense breast tissue. An X-ray mammogram can identify a suspected tumor in younger women, but invasive removal of tissue is needed from the suspected region for a biopsy to determine whether the tissue is cancerous or benign.
A more recent, and less invasive, technique for breast cancer detection is optical mammography. This technique uses near infrared (NIR) light to identify concentrated amounts of hemoglobin. Tumors generate blood vessels and therefore tend to have more blood and more hemoglobin, which is a natural but strong chromophore in tissue. This results in high absorption of NIR light. Optical mammography methods can detect tumors as small as 0.5 mm.
However, this technique can fail to identify tumors that are particularly small or deep-seated within the breast. Such tumors have weak optical contrast and are still difficult to detect. In the case of very small and/or deeply seated tumors, additional contrast may be needed for detection. Such additional contrast can be achieved by using fluorescing contrast markers.